This invention relates to electrochemistry and, more particularly, to novel and highly-effective processes for producing electric current utilizing electrochemical reactions and to generators for use in such processes.
Such generators comprise at least one cell having at least one anode compartment and one cathode compartment.
The invention concerns, in particular, generators of this type which comprise a compartment containing a liquid electrolyte within which particles are contained, the electrolyte and the particles being in movement. This compartment comprises a so-called "electron-collector" member which is a conductor of electricity and is intended to collect the electric charges liberated during the electrochemical reaction carried out in the compartment or to deliver the electric charges necessary for this reaction.
The expression "particles" is employed in a very broad sense and designates solid particles, liquid or pasty drops, or gas bubbles, the drops or bubbles forming, for instance, liquid or gaseous emulsions in the electrolyte, or mixtures of any of these.
The particles may furthermore be formed in their entirety of a material which participates in the electrochemical reaction, i.e. so-called "active material".
The particles may on the other hand be partially active and/or serve as support for at least one active material. This is true in particular both of particles containing this active material in the state of a solution, alloy, or amalgam and of particles whose electrochemically inactive center, which is for instance solid, is covered by such active material, the particulate supports then permitting the transport of the active material and possibly serving as catalysts.
In all cases, the active material may be present in any physical state--solid, liquid, or gaseous--, and its chemical composition may be any whatsoever, for instance a metal, oxygen, hydrogen, a halogen, or an inorganic or organic compound, in particular an oxide, a salt, a hydrocarbon, an alcohol, an acid, an amine, or a mixture of these active materials.
The electrochemical reaction in which the active material participates may take place in anode compartments, the active material being then sometimes referred to as "fuel", or in cathode compartments.
The invention concerns more particularly generators in which there is created, through at least one of the compartments, a flow of a liquid electrolyte containing particles in accordance with the preceding definition which are in intermittent contact with the collector so as to favor the diffusion of the active material or of the products resulting from the electrochemical reaction. In order to increase the specific power of these generators, U.S. patent application Ser. No. 821,760, now U.S. Pat. No. 4,092,461, filed concurrently herewith, entitled "Electrochemical Generators with a Sedimentation Bed", discloses creating in the compartment a flow such that the particles, whose density is greater than that of the electrolyte, are solid and form a sedimentation bed contiguous to the lower face of the compartment, the surface of the lower face being formed at least in part by all or part of the surface of an electron collector arranged on the electrolyte side.
The particles which thus, because of their weight, become concentrated in the vicinity of the lower face of the compartment within a space known as the "sedimentation bed" are entrained by the electrolyte.
The movements of the particles within the sedimentation bed assure a substantial current density while facilitating the diffusion phenomena. For this purpose, it may be advantageous to provide the lower face with elements in relief arranged above a base surface, said base surface being possibly at least in part immaterial. In the following, the expression "lower face" of the compartment designates either the actual surface of the face (when it does not have any elements in relief) or its base surface (when it does have elements in relief), the expression "surface" of the lower face designating its actual surface.
In order suitably to form such a sedimentation bed, it is disclosed in that application that any normal to the lower face of the compartment, which normal is oriented towards the electrolyte, forms a small or zero angle, and in any event an angle of less than 90.degree., with the ascendant vertical.
In order to facilitate the formation of the sedimentation bed, the side faces may, in the vicinity of the inlet of the compartment, form an angle which diverges in the direction of flow, which angle is preferably equal to at most 20.degree.. In order to facilitate the entrainment of this bed through the compartment, the upper and lower faces of the compartment can form an angle with converges in the direction of flow, which angle is preferably equal to at most 10.degree..
For the same purpose, the side faces of the compartment may, in the vicinity of the outlet of the compartment, form an angle which converges in the direction of the flow, this convergent angle being preferably equal to at most 20.degree..
When the formation of the sedimentation bed in the vicinity of the inlet to the compartment can be obtained without divergence in the compartment, it may possibly be advantageous to have the side faces converge over the greater part of the compartment or over the entire compartment.
The principal parameters involved in the formation of the sedimentation bed are as follows:
d.sub.0 = density of the particles
d.sub.1 = density of the electrolyte
D = average diameter of the particles in the electrolyte
u = average speed of flow in the compartment, that is to say the ratio: ##EQU1## this average cross section being measured perpendicular to the average direction of flow in the compartment and at a point located substantially at the center of the compartment
.mu. = viscosity of the electrolyte
e = average distance between the lower and upper faces of the compartment
L = average length of the compartment
l = average width of the compartment
e, L, l being measured at a point located substantially at the center of the compartment, the measurement being made perpendicular to the lower face in the case of e, parallel to the average direction of flow in the compartment in the case of L, and perpendicular to that direction in the case of l
R = Reynolds number = 2 d.sub.1 e u/.mu.
v/V = ratio between the total volume v of the particles and the total volume V of electrolyte in the compartment at any given moment.
Preferably, d.sub.0 is at least equal to 2.5; d.sub.1 is at most equal to 1.6; D is at least equal to 30 microns; u is between 5 m/minute and 60 m/minute; e is at most equal to 1 cm; the ratio l/e is at least equal to 10; L is between 10 cm and 1 m and varies in the same direction as the ratio ##EQU2## in which a, b, c, d and 2f are positive exponents; R is at most equal to 4,000; v/V is at most equal to 0.30; .mu. is at most equal to 0.01 poiseville.
Even more preferably, d.sub.0 is at least equal to 4; d.sub.1 is at most equal to 1.4; D is at least equal to 40 microns; u is between 10 m/minute and 30 m/minute; e is between 1 mm and 5 mm; l/e is at least equal to 20; L is between 20 cm and 60 cm; R is at most equal to 3,000; v/V is at most equal to 0.15; and .mu. is at most equal to 0.005 poiseville.
It may be necessary to connect in series at least two sedimentation bed chambers. One of these chambers is an electrochemical compartment, previously defined, referred to as the "sedimentation bed" compartment, and the other may be either another electrochemical compartment or a chamber without electron collector, and in particular a feed chamber.
When this series connection is effected without any particular precaution there is a disturbance in the sedimentation bed in the downstream chamber and it is necessary to reconstitute the sedimentation bed in an additional device before introducing the electrolyte and the particles into the chamber. This device, for instance one of the devices described in U.S. patent application Ser. No. 821,759, filed concurrently herewith, entitled "Electrochemical Generators with a Sedimentation Bed and Divergent Feed", increases the size and the price of the generator.
The difficulty in connecting chambers in such a manner that they are traversed in series by a liquid electrolyte containing particles is moreover present even if there is no sedimentation of the particles in the chambers and even if the particles are not solid, since the disturbance in the flow generally are transmitted from one chamber to the other.